Features. Conference Report: NOx, SO3 in the spotlight at NETLNETL's 2006 Environmental Controls Conference

Power, Feb 2007 by Mann, Alfred N, Makovsky, Leo E, Inc, Management Services, Sarkus, Thomas A, Laboratory, National Energy Technology

face= Bold; Improving SCR performanceface=-Bold;

A novel way to enhance SCR system performance was described by D. Broske of EPRI and L. Muzio, D. Shore, J. Muncy, and T. Martz of Fossil Energy Research Corp. They explained that inter-layer mixing is very effective at maintaining uniform distribution of flue gas and reagent, markedly improving the efficiency of NOface= Subscript; xface=-Subscript; reduction. Brad Adams and Connie Senior of Reaction Engineering International (REI) showed how computational fluid dynamics (CFD) can be used to model the various sections of an SCR system to optimize gas flow patterns, with beneficial impact on system performance.

The impact of SOface= Subscript; 3face=-Subscript; formation on SCR systems serving units burning high-sulfur coals (a subject covered in greater detail in the SOface= Subscript; 3face=-Subscript; session of ECC 2006 ) was discussed by Bill Ellison, PE, of Ellison Consultants (and one of POWER's contributing editors), Volker Rummenhohl of TackTicks LLC, and Helmut Weiler of Weiler Consultants. They recommended using SCR catalysts with low SOface= Subscript; 2face=-Subscript; oxidation rates, injecting alkali upstream of the air preheater, and a number of other measures to minimize corrosion.

The presence of large-particle ash (often referred to as popcorn ash) has become a serious concern for many operators of coal-fired boilers equipped with high-dust SCR systems. A paper presented by Hans Sobolewski, Hans Hartenstein, and Marilynn Martin of Steag, and Joseph Jancauskas and Michael Harrell of Dayton Power & Light's J.M. Stuart Station, described the successful use of specially designed screens to continuously remove popcorn ash (see box).

face= Bold; New approaches to NOface= Subscript; xface=-Subscript; controlface=-Bold;

Several alternatives to SCR and SNCR are being explored, with a view to reducing the overall costs of NOface= Subscript; xface=-Subscript; reduction. One concept is to use a hybrid SCR/SNCR system, to reap the benefits of each technology. In one approach, Dale Pfaff of Fuel Tech Inc. and Richard Abrams of Babcock Power Environmental described the combination of a two-stage, urea-based SNCR system with in-duct SCR operation. Another hybrid system was proposed by Thomas Wright and James Cox, mechanical engineers with WorleyParsons Group.

A second approach, involving the use of carbon moNOface= Subscript; xface=-Subscript; ide (CO) rather than ammonia as the reductant, was proposed by Zhen Fan and Andrew Seltzer of Foster Wheeler North America Corp., Richard Herman of Lehigh University's Energy Research Center, and Kamalendu Das of NETL. In this novel concept, the reduction/oxidation (redox) reaction is catalyzed by a base metal catalyst, which absorbs SOface= Subscript; 2face=-Subscript; as well as mercury. It has been tested on a bench-scale reactor, and further studies are under way using CFD simulations.

Two other papers described alternative approaches to NOface= Subscript; xface=-Subscript; control. Both involve maximizing the use of layering (staging) and low-NOface= Subscript; xface=-Subscript; burners and overfire air to minimize the load on the final reaction step. A paper by Charles Trippel, PE, and Peter Marx, PE, of Advanced Combustion Technology Inc.; Dick Carlow of Blue Ridge Paper Products; and Robert Durso of NRG Middletown Power LLC covered one approach.